Recent work in several countries has been conducted on radiation annealing to return amorphous semiconductor surface regions to the crystal state. In particular, if the radiation source is a laser capable of melting the semiconductor to a depth at least equal to the depth of the amorphous surface region, it has been shown by many workers in the art that the molten region will regrow epitaxially on the unmelted crystal substrate, thus returning the molten region to the crystal state. "Laser Annealing of Implanted Silicon," O. G. Kutukova and L. N. Streltsov, Sov. Phys. Semicond., 10, 265 (1976); "Spatially Controlled Crystal Regrowth of Ion Implanted Silicon by Laser Irradiation," G. K. Celler, J. M. Poate and L. C. Kimerling, Appl. Phys. Lett., Vol. 32, No. 8 (Apr. 15, 1978).
It is also known that diffusion of dopant atoms in silicon proceeds very rapidly while the silicon is in the molten state. "Time-Resolved Reflectivity of Arsenic-Implanted Silicon During Laser Annealing," D. H. Auston, C. M. Surko, T. N. C. Venkatesan, R. E. Slusher, and J. A. Golovchenko, Appl. Phys. Lett., Vol. 33, No. 5 (Sept. 1, 1978), p. 437.
Further, it is possible for a change in dopant distribution to occur as the liquid-solid interface moves through the material during resolidification, due to the difference of solubility of the dopant atoms in the liquid as compared to the solid semiconductor. This effect is referred to as segregation of impurities. "Distribution of an Implanted Impurity in Silicon after Laser Annealing," A. Kh. Antonenko, N. N. Gerasimenko, A. V. Dvurechenskii, L. S. Smirnov, and G. M. Tseitlin, Sov. Phys. Semicond., Vol. 10, p. 81 (1976); "On the Mechanisms of Impurity Redistribution at The Laser Annealing of Ion Implanted Semiconductors," A. V. Dvurechensky, G. A. Kachurin, A. K. Antonenko, presented at the U.S.-U.S.S.R. Seminar on Ion Implantation, July 4-6, 1977, Albany, N.Y.
In addition, both the diffusion and segregation effects have been observed when a semiconductor device (a phototransistor) was subjected to laser radiation. "Observation of Impurity Migration in Laser-Damaged Junction Devices," C. L. Marquardt, J. F. Giuliani and F. W. Fraser, Radiation Effects, Vol. 23, pp. 135-139 (1974); "Electrical Effects in Laser-Damaged Phototransistors," J. F. Giuliani and C. L. Marquardt, Journal of Applied Physics, Vol. 45, No. 11, pp. 4993-4996 (November 1974). This work was also the basis of U.S. Pat. No. 3,940,289 granted to C. L. Marquardt and J. F. Giuliani, entitled "Flash Melting Method for Producing New Impurity Distributions in Solids." The Marquardt patent teaches primarily the use of the segregation effect at the solid-liquid interface to obtain impurity redistribution.
The usefulness of localized dopant redistribution to change p-n junction geometries can be appreciated by reference to semiconductor devices in which the magnitude of an electric field defines important parameters of operation. For example, the reverse breakdown voltage of zener or avalanche diodes depends on, among other things, the electric field in the junction. The electric field in turn depends on the geometry of the junction. Also, it is well known that for stable, low-noise operation, the breakdown in such diodes should occur in the buried region of the junction, away from the surface. It would be useful therefore if a technique were available whereby a portion of the p-n junction residing in the buried region could be selectively deformed, changing the electric field for a given applied voltage, and hence changing the breakdown voltage.
The channel width of a junction field effect transistor has an important effect on the pinch-off voltage and other parameters of operation of the device. It would be useful therefore if a portion of the channel width could be tailored to almost any desired configuration. In another area of possible application, the prior art teaches the use of buried doped regions in making various semiconductor devices. However, making ohmic contact to such regions may require such time-consuming steps as etching away a small portion of the overlying material and making metallic contact. It would be very useful if a conducting channel could be rapidly formed from an overlying region to the buried regions, or between buried regions. Also, for such uses as large scale integration where different areas of the chip are used for different functions, it would be very useful to be able to rapidly isolate regions by a p-n junction.